1. Technical Field
This invention is directed to a method and apparatus for illuminating electro-optical devices, a more specifically to projection system that uses optical fibers to distribute light.
2. Background Art
By far the most popular large-screen device is the projection display. Historically the source of the image was a cathode ray tube, and recently there has been great strides made with microdisplay imagers, both transmissive and reflective. Recently, JVC introduced a state-of-the-art liquid crystal on silicon (LCOS) imager, 1.3″ diagonal device with 1920×1080 pixels. For resolutions higher than this, a tiled system would be employed. For example, Olympus Optical Co. has developed a tiled projection system using nine projectors, each 600×800 in a 3×3 matrix to create a 100″ diagonal display with 2400×1800 pixels, with a price tag of $200,000 each. Alternately, Clarity Visual Systems promotes modular, stackable, projection elements, although not seamless.
Plasma displays have made some inroads in the high definition television (HDTV) market, with the largest displays at 50″ in diagonal—the PlasmaSync 50MP1 from NEC with a resolution of 1,365×768 and weighing 101 pounds, and the Pioneer PDP-502MX, with a resolution of 1280×768, weighing in at 88 pounds—each retailing for more than $10,000. State of the art liquid crystal displays (LCDS) from Samsung and others are approaching 30-inch diagonals, with resolutions far surpassing that of plasma displays. For direct view sizes (and resolutions) higher than this, a tiled system would be employed. For example, Rainbow Displays has developed a tiling approach using a collimated backlight, custom LCDs with narrow borders, and a single projection screen placed across all devices.
A unitary projector or direct-view display cannot meet size and resolution requirements. Therefore, the option exists for a tiled-solution. All tiled systems must resolve perceived differences between tiled elements, e.g., luminance and chrominance uniformity for all gray shades over all viewing angles. To effect seamless operation, any perceived border between tiles must be eliminated, thereby adding additional complexity, especially when the pixel pitch at the viewing surface is less than a few millimeters.
Both projection- and direct-view tiling systems have the following cost disadvantages when compared with a unitary display.                1. The need for additional components, such as optical masks and feedback systems, that need to be inserted to hide the seams.        2. Niche-market status, leading to high recurring cost since the investment for lower cost solutions does not have adequate payback time.        3. Labor hours to accurately align tiles and calibrate the system during assembly.        
Both projection- and direct-view tiling systems have the following performance disadvantages when compared with a unitary display.                1. Non-uniformities between tiled elements induced by minor differences between components in one or more of the tiles. For example, display device electro/optical characteristics, lamp aging characteristics, etc.        2. Loss of dynamic range by using gray shades to compensate for non-uniformities between tiled elements.        
Projection-based tiled systems have the following cost disadvantages when compared with systems that employ a unitary projector.                1. Concentrated heat load in the volume around the projector array, necessitating special room-cooling considerations        2. Concentrated fan-noise in the volume around the projector array, necessitating special sound-dampening considerations        3. Maintenance costs involved in replacing lamps suspended near the ceiling, especially for the projectors in the middle of the array that may be hard to access        4. Need for a feedback control system to ensure alignment between tiled elements        5. Higher ambient temperatures for any projector located above another projector, potentially requiring temperature stabilization of the imaging elements to ensure uniform contrast and response time between tiled elements        
Projection-based tiled systems have the following performance disadvantage when compared with systems that employ a unitary projector.                1. Differences in thermal expansion between tiled elements as a result of temperature gradients that differ between one or more units, thereby causing misalignment between tiles over time unless periodic re-calibration is employed        
Direct view tiled systems have the following cost disadvantage when compared with systems that employ a unitary projector.                1. Special LCDs must be fabricated that employ unusually narrow dead-zones around periphery of the active display area        
Direct view tiled systems have the following performance disadvantages when compared with systems that employ a unitary projector.                1. Resolution limitations for seamless systems; practical limits of a mechanical seam appear to be on the order of 1 mm.        2. Differences in thermal expansion between tiled elements as a result of temperature gradients that differ between one or more units, thereby causing stress, which could lead to either structural fatigue (mechanical failure) or stress-induced birefringence (optical non-uniformities)        3. Inherent mechanical limits for a very large area glass structure, thereby reducing the practicality of arranging such systems.        
One way to achieve very large area displays with very high resolutions is through tiling. However, the cost/performance trades of such systems, even when combined with prior inventions in the art, will continue to result in niche market status. There is a known demand for high-definition, seamless, large screen displays for such applications as advertising, theaters, and media-centers for the government, corporations, and the television broadcast industry. Specifically, there is a need for tiling approaches that achieve the full performance characteristics of a unitary device at low cost.